Automatic exchange



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AUroMATrC EXCHANGE Maurice Mose Levy, Ottawa, Ontario, Canada, assignor to The General Electric Company Limited, London, England, a British company Application November 23, 1951, Serial No. 257,786

Claims priority, application Great Britain November 23, 1950 3 Claims. (Cl. 179-15) The present invention relates to automatic exchanges for telephony and the like.

In co-pending patent application Ser. No. 247,072, filed September 18, 1951, there is described an improved automatic exchange in which a fixed plurality of communication channels is provided. Calling apparatus responsive to an initial calling signal such as a D. C. signal transmitted when a telephone subscribed lifts a telephone handset'prior to dialling the number of another subscriber, selects a free one of the aforesaid communication channels. Means are provided whereby, in operation, further calling signals, such as dialling impulses, are then applied in the exchange to transmit to the terminal equipment of the called subscriber an identification signal identifying the selected one of the communication channels, lnteirogating apparatus is provided to identify the channel indicated by the identification signal and to conneet the called subscriber to the identified channel.

in order to route the identification signal to the called subscriber suitable routing apparatus is provided and one form of routing apparatus is described in co-pending patent application Ser. No. 247,233, filed September 19,

According to the present invention, an automatic exchange comprises a first group of communication channels, the channels being of low grade, the number of channels being at least equal to the number of stations connected to the exchange, and different channels being identified with different ones of the stations connected to the exchange, a second group of communication channels comprising a relatively small number of high grade channels, calling apparatus responsive to an initial calling signal from a calling station to seize a free one of the high grade channels, means responsive to further signals from the calling station and representative of the numbei' of z. called station to establish a connection with the low grade channel identified with the called station and to transmit in the last-named channel to the called station an identification signal representative of the said selected high grade channel, and apparatus responsive to the said identification signal to connect the called station to the said selected high grade channel. A station may be, for example, a telephone handset, telegraph apparatus, or another exchange. A low grade channel is a channel having a relatively small bandwidth, say a few cycles per second, whereas a high grade channel is a channel 'having a relatively large bandwidth, say a few thousand cycles per second. seizes a free high grade channel it is meant that the calling apparatus finds a free high grade channel, establishes a connection therewith and further calling stations are prevented from making use of this channel to establish another call until the channel is freed.

The two groups of communication channels are preferahly provided by time sharing pulse trains but may be provided in any suitable manner. The frequency of the pulses in the trains of the first group may be say only a small number of pulses per second, and the frequency When it is said that the calling apparatus 2,754,367 Patented July 1o, 195e ICC 2 of the pulses in the pulse trains in the second group ma; be, say 8000 pulses per second if speech is to be transmitted.

The invention will now be described, by way of example with reference to the accompanying drawings, in which:

Figure l is a block schematic diagram of one embodiment of the invention,

Figures 2 to 12(5) are diagrams of parts shown in block 'form in Figure 1, and

Figure V13 is an explanatory diagram,

Figures 14 and 15 are diagrams of further parts shown in block form in Figure 1,

Figure 16 is a further explanatory diagram, and

Figure 17 is a diagram of a gate circuit.

Referring to Figure l this is a block schematic diagram of 'an Vautomatic exchange suitable for use with 2,000 lsubscribers. Of the 2,000 subscribers stations connected to the exchange, one is shown at 10 and another at 11,v the station 10 being terminated in the exchange at subs-'line circuit 12 and the station 11 being terminated at the ,subs line circuit 13. The subs line circuits will be described later.

The exchange comprises a group of high grade pulse communication channels. This group of channels is provided by means including a pulse generator 14 adapted to generate pulses suitable for combination to provide the 100 channels time-interlaced at a pulse repettion frequency-of 8,000 pulses per second in each channel. The 100 'channels are terminated by 100 calling units respectively'of which one is shown at 15. 100 called units terminate the other ends of the channels respectively when in use one of the called units being shown at 16.' The calling and called units will be described later. Signals between the calling and called units pass through a GO speech junction 17, a Return speech junction 18 or a Metering and release junction 19 as the case may be. ln the event of a called subscriber being engaged, a busy signal is transmitted to the calling subscriber by way of a busy junction 20 as will be described later.

For use in establishing calls between subscribers a number of allotters 24 and registers 23 are provided together with a signalling junction 25 and two further pulse generators 21 and 26, examples of which will be described ater.

Assuming the subscriber at station 10 to be calling the subscriber at station 11, the first operation occurs in the subs line circuit 12. This contains a finder which finds a free calling unit 15. An allotter 24 then comes into operation and allots a register 23 to the calling unit 15.

By means of the allotter and a finder in the register the calling unit found by the subs line circuit 12 is connected to the allotted register 23 as will be described later. A dialling tone is then automatically transmitted to the calling subscriber.

The output of the pulse generator 21 is in the form of a recurring sequence of twenty pulses which for convenfence will be divided into two groups of ten each. The first ten pulses in each sequence will be referred to collectively-as. the d pulses and the second ten as the u pulses. The ten d pulses will be referred to individually as pulses d'0 to d'9 respectively and appear at the terminals Td'o to Tds of the generator 21. The ten u pulses will be referred to individually as pulses uo to ug and appear at terminals Tuo to Tus of the generator Each calling unit 15 is connected to one of the terminalsTdo to Tdfg and to one of the terminals Tu'o to Tus of the generator 21 different ones. of the calling units being connected to different pairs of the terminals Tdf and' Tu'. Thus each calling unit is identified by a different pair of d and u pulses and, as will be described later, the pair of d' and u' pulses identifying the calling unit seized by a calling subscribers line circuit is transmitted to the called subscribers line circuit to identify the high grade channel on which communication is to be established.

When the calling subscriber hears the dialling tone and ials the number of the called subscriber, the dialling pulses are transmitted through the line circuit 12, and the seized calling unit to the allotted register 23. In the register the four sets of dialling pulses are stored on four uniselectors as will be described later. Four groups of ten pulse each, which will be referred to as the M, C, D and U pulses, are applied to the four uniselectors in the register from the pulse generator 26. Thus the uniselectors in the register select one pulse from each of the four groups of recurring pulses applied thereto and it is arranged that these four selected pulses are combined to forma recurring output pulse which recurs in one recurring channelY interval in a recurring sequence of 2,000 channel intervals. The sequence may recur for exampleat the rate of one per second and the 2,000 channels constitute a group of low grade communication channels.

The recurring output pulse from the register is used as a gating pulseand permits the recurring pair of d'u' pulses identified with the seized calling unit to pass to a signalling junction 2S only in the low grade channel interval determined by the gating pulse.

The output from the signalling junction is applied to all subscribers line circuits. These circuits have gating pulses applied thereto, however, from the pulse generator 26, the gating pulses applied to each subscribers line circuit being in the channel Whose number corresponds to the subscribers number on the exchange. Thus the only subscribers line circuit to respond to a pair of d u' pulses appearing at the output of the signalling junction is that one whose gating pulse corresponds to the number dialled.

The called subscribers line circuit then hunts for a free called unit and when a free called unit is found this unit functions, as Will be described later, to select appropriate pulses from the output of the generator 14 to enable the'called subscriber to establish communication on the channel terminated by the seized calling unit.

TheV automatic exchange shown in Figure l will now be described in more detail with reference to Figures 2 to 17. Throughout Figures 2 to 17 all relays and automatic switches are shown in conventional manner the operating windings thereof being referenced with a letter over a gure, the figure indicating the number of relay contacts or banks of switch contacts associated with the winding. The contacts or banks of contacts associated with a winding are given the same letter reference followed by a figure, references to different contacts or banks of contacts containing different figures. A contact may also have the same reference letter as its operating winding followed by a further letter or letters. All relays and switches are shown in their unoperated positions.

Referring to Figure 2 this is a circuit diagram of apparatus suitable for use as the subs line circuits 12 and 13 of Figure 1. The subscribers line is connected to line terminals LT1 and LTz, LT1 being normally connected to'earth through relay contacts K1 and LTz being normally connected through relay contacts K2, relay winding L and battery BAT1 to earth. A uni-selector having six banks of contacts S1 to Ss is operated by a winding S and interruptor Sdm. The automatic interruptor operation may be as described on page 225 of Telephony, volume 2, by J. Atkinson, published by Sir Isaac Pitman & Sons, Ltd., 1950. This work by Atkinson will be herein- The banks S1 and S2 are for carrying speech, the wipers thereof being connected to LT1 and LTz respectively when the apparatus is in use, by relay contacts K1 and K2. Contacts 2 to 13 of S1 are connected to l2 output terminals respectively of which one is shown at +01, and contacts 14 to 25 are connected to l2 input terminals respectively of which one is shown at +I1. Contacts 2 to 13 of S2 are connected to l2 output terminals of which one is shown at +01, and contacts 14 to 25 are connected to l2 input terminals of which one is shown at -l1. The bank S3 is used for control purposes, contacts 2 to 13 being connected to 12 output terminals respectively of which one is shown at P01, and contacts 14 to 25 being connected to l2 .input terminals of which one is shown at P11.

Bank S4 has an insulated home contact and a homing arc BC1. The function of the homing arc is as described on pages 25S and 260 of Telephony, vol. II, by Atkinson.

Bank S5 has an insulated home contact, anV arcuate contact BC2 extending over the equivalent of contacts 2 to 13 on S1, S2 and S3, and a further arcuate contact BC3 extending over the equivalent of contacts 14 to 25 on S1, Sz and Ss. Contact BC2 is connected through relay contacts Zz to earth.

Bank Ss has an insulated home contact, an arcuate contact BC4 extending over the equivalent of contacts 2 to 13 of S1, S2 and Ss, and a further arcuate contact BC5 extending over the equivalent of contacts 14 to 25 on S1, S2 and S3. Contact BCs is connected to an output terminal CS1.

The home contact on S3 is connected through relay contacts L1 to earth. The wiper of S3 is connected through contacts K3 and L1 to earth through contacts L2, and K4 to contacts Sdm; and through a rectifier W1 and meter Winding M to earth.

The wiper of S4 is connected through contacts L2 to contacts K4 and to the Wiper of S5.

The wiper of Ss is connected through relay contacts K7 to an input terminal RT. This terminal is connected through relay contacts Ks to an output terminal B11 and through resistors R1 and R2 and a rectifier WXi in series to the control grid of a gas-filled triode valve V1 the control grid being connected to earth through a capacitor CX1. An input terminal SX1464 is connected through a rectifier W2 to the junction of resistors R1 and R2. The cathodelead of the valve V1 has in series therewith a relay winding Z and the anode of the valve V1 is connected through relay contacts K5 to the terminal HT+l of a source (not shown) of D. C. whose negative terminal is earthed. A relay winding K is connected between contacts Sdm and L1.

Referring now to Figure 3 this is a circuit diagram of apparatus suitable for use as the calling unit 15 of Figure l. It will be assumed that this calling unit is that connected to terminals +01, -01 and P01 of Figure 2, these terminals also being shown in Figure 3. Terminal +01 is connected through relay contacts D1 and one Winding of a relay A to earth. Terminal O1 is connected through relay contacts D2, a second winding lof relay A and a battery BATs to earth. Terminals +01 and -O1 are also connected through capacitors C1 and C2 respectively to a winding MW1. of a hybrid transformer HY1 which has a balancing resistor RB. The function of the hybrid transformer and Ybalancing resistor is as described on page 83, vol. I of Telephony, by Atkinson.

The winding OW1 of the hybrid transformer is connected through a capacitor C3 to the control grid of a pentode valve V4 whose Aanode is connected through a load resistor R3 to the positive terminal HT+2 of a source (not shown) of D. C. whose negative terminal is earthed. The cathode of the valve V4 is earthed, the screen grid is connected directly to the terminal HT+2, and thesuppressor grid is connected through a resistor R4 to thenegative terminal -GB1 of a bias source (not shown) whose positive terminal is earthed. The `suppressor grid is also connected through a capacitor C4 and relay contacts B5 to a terminal GP. The anode of the valve V4 is connected through a capacitor C5 to a terminal GSP.

Winding IW1 of the hybrid transformer HY1 is connected to the output of a low-pass filter FIL1. One input terminal of the lter is connected to the anode of a pentode valve V3 and the other to earth through a capacitor Cs and through a resistor R5 to the positive terminal HT+3 of a source of D. C. (not shown). The suppressor grid and cathode of the valve V3 are connected to earth.

A terminal RSPO1 is connected through a capacitor Cs to the control grid of a pentode valve V5 whose cathode s earthed. Negative bias is applied to the control grid of the valve V5 from'the negative terminal GB2o of a bias source (not shown) whose positive terminal is earthed. The anode of the valve V5 is connected through the primary winding of a transformer XF1 to the positive terminal HT|4 of a source (not shown) of D. C. whose negative terminal is earthed. The screen grid of the valve V5 is connected directly to the terminal HT|4 and the suppressor grid is connected through a resistor Re to the negative terminal -GBs of a bias source (not shown) whose positive terminal is earthed. The suppressor grid of the Valve V5 is also connected through a capacitor C9 and the contacts B5 to the terminal GP.

The transformer XF1 has two secondary windings S1XF1 and S2XF1. One terminal of winding S1X.F1, is connected to the negative terminal -GB2 of a bias source (not shown) and the other terminal is connected through a rectier W5, and a resistor R7 to the control grid of the pentode valve V3 and is connected through a recitifer W3 to the negative terminal -GB4 of a bias source (not shown) whose positive terminal is earthed. One terminal of the winding S2XF1 is connected to the negative terminal -GB4 and the other terminal of the winding S2XF1 is connected through a rectifier Ws to the control grid of the valve V3. The terminal -GB4 is also connected to the control grid of V3 through a rectifier W4 and a capacitor C10 is connected between the control grid of V3 and earth.

A terminal ASPO1 is connected through a rectifier W1 and capacitor C11 to the control grid of a triode valve Vs whose cathode is earthed and whose anode is connected through a relay winding D to the positive terminal HT-i-S of a D. C. source (not shown) whose negative terminal is earthed. The control grid of the valve Vs is also connected through a rectier We to the negative terminal -GBs of a bias source (not shown) whose positive terminal is earthed. The junction of the capacitor C11 and the rectier W7 is connected to the terminal GP through a resistor Ra.

A relay winding J has one terminal connected to earth through a battery BAT4. The other terminal of the relay winding l is connected to earth through relay contacts Da, a busbar BUSi and relay contacts B4. The busbar is connected through relay contacts E1, one windingof relay E and a battery BATs to earth. A control terminal P1 is connected either directly to earth or through the other winding of relay E and a battery BATS to earth depending upon the setting of relay contacts B3 and E3. The busbar BUS1 is connected through relay contacts G1, one winding of a relay G and a battery BAT'z to earth. The other winding of the relay G has one terminal connected to earth through a battery BATS, and has its other terminal connected directly to a terminal BU1. The busbar is also connected through relay contacts E2 t0 an output terminal AL.

Terminal HO is connected through relay contacts Ds, Es and A1 to earth. A relay winding B has one terminal connected through contacts A1 to earth and the other through a battery BAT9 to earth. An output terminal- IMP is connected through relay contacts B2' and A1 to earth.

Input terminals Tdo and Tu1 are connected together through resistors R9 and R10 and the junction of these two resistors is connected through relay contacts Es to an output terminal Rdu.

Terminal P01 is connected through relay contacts B1 to relay contacts D4 which depending upon their-setting, provide either an earth connection or a connection to relay contacts I1. The relay contacts J1 provide either an earth connection or a connection through a resistor R11 and a battery BATio to earth.

The cathode of a gas-lled triode valve V2 is connected to earth through relay contacts A2 and its anode is connected through a relay winding F to the positive terminal HT-tof a suitable source (not shown) of D. C. Whose negative terminal is earthed. A capacitor VC12 is normally connected to the positive terminal HT-i-7 of a source (not shown) of D. C. whose negative terminal is earthed. The control grid of the valve V2 is connected to the capacitor C12 through a resistor R12 and the contacts E5.

A source (not shown) of busy tone is connected to the terminal BT which is connected to the centre winding of the relay A through relay contacts G2.

A source (not shown) of dialling tone is connected to the terminal DT which is connected through relay contacts F1 to the centre winding of the relay A.

Referring now to Fig. 4, this is arcircuit diagram of an allotter suitable for use at 24 in Fig. l. The terminal AL corresponds to the terminal AL of Fig. 3 and is connected through a relay winding ST and a battery BAT11 to earth. A uni-selector FD has four banks of contacts FD1, PD2, FDa and FD@L Whose wipers are controlled by automatic stepping apparatus including winding FD and contacts FDdm. The wiper of the bank FDi is connected through relay contacts ST1, the contacts FDdm the winding FD and a battery BAT12 to earth. The junction of the contacts FDdm and the winding FD is connected to earth through relay contacts FKz and DRi. The fixed contacts of the bank FD1 are connected to output terminals respectively of which one is shown at Q. A terminal R is connected through a relay winding DK and relay contacts ST2 to the moving contact of the bank FD1. The terminal R is also connected through contacts ST3, and DK1 to contacts ST1. The contacts DK1 are also connected through relay winding DR and a battery BAT13 to earth.

The bank contacts of the bank FD4 are connected to output terminals respectively of which one is shown at X. The wiper of the bank FDL; is connected through reiay contactsv DRS, FK1, and DR1 to earth.

The xed contacts of the bank FDs are connected to output treminals respectively of which one is shown at P2. The wiper of the bank FDa is connected through relay contacts DRz and one winding of relay PK to earth. One terminal of the other winding of the relay FK is connected through the contacts FK1 and DR1 to earth, and the other terminal thereof is connected through a battery BAT14 to earth.

rne bank contacts of the bank PD2 are-connected to output terminals respectively of which one is shown at Y. The wiper of PD2 is connected through the contacts FKr and DR1 to earth.

Referring now to Fig. 5 this is a theoretical circuit diagram of a suitable register and calling unit nder'for use in the arrangement of Fig. l. The terminals IMP, ldzz, BUi, HO, and P1 correspond to the terminals of the same reference in Fig. 3, and terminals Y, P2, X, R and Q correspond to those of the same reference in Fig. 4.

The calling unit nder section of the arrangement shown in Fig. 5 comprises a uniselector CUF having -six banks CUF1 to CUPS, whose wipers are driven byan automatic stepping circuit including Va battery BATis connected between earth and oneterminal of winding 

